1. Technical Field
The present invention relates to a vehicle driving apparatus in which a driving device for driving a left wheel and a driving device for driving a right wheel are separately provided.
2. Related Art
WO 2011/013829 and Japanese Unexamined Patent Application Publication No. 9-79348 each disclose a vehicle driving apparatus including: a left wheel driving device having a first motor for driving a left wheel of a vehicle, and a first planetary gear transmission provided on a power transmission path between the first motor and the left wheel; and a right wheel driving device having a second motor for driving a right wheel of the vehicle, and a second planetary gear transmission provided on a power transmission path between the second motor and the right wheel. The first and second motors are connected to sun gears of the first and second planetary gear transmissions, respectively, the left wheel and right wheel are connected to planetary carriers of the first and second planetary gear transmissions, respectively, and ring gears of the first and second planetary gear transmissions are connected to each other. Further, the vehicle driving apparatus is provided with: a hydraulic brake that is released or engaged, thereby braking rotations of the connected ring gears; and a one-way clutch which is provided in parallel with the hydraulic brake and through which the rotations of the ring gears in one direction are allowed and the rotations of the ring gears in the reverse direction are restricted.
In the apparatus disclosed in WO 2011/013829, when forward rotation power from the motors is inputted to the wheels to move the vehicle forward, the one-way clutch is engaged, thereby allowing the rotational power from the motors to be transmitted to the wheels. On the other hand, when forward rotation power from the wheels is inputted to the motors, the one-way clutch enters a non-engaged state, thereby preventing the power from the wheels from being transmitted to the motors. Furthermore, when regeneration is carried out by the motors by using the rotational power from the wheels, the hydraulic brake is engaged, thereby transmitting the rotational power from the wheels to the motors.
In the apparatus disclosed in WO 2011/013829, in controlling rotational frequencies of the ring gears to change a connection/disconnection means from a released state to an engaged state when the forward rotation power from the wheels is inputted to the motors, driving control is performed on both of the left and right motors, i.e., the first and second motors, so that target rotational frequencies are achieved.
Referring to FIGS. 27A to 27D and FIG. 28, the above-described control will be specifically described using an example in which the vehicle is making a turn (left turn). When the vehicle makes a left turn by front wheel driving carried out by a front wheel driving apparatus, a rotation difference occurs between right and left rear wheels, so that the motor for driving the left rear wheel is rotated in the reverse direction and the motor for driving the right rear wheel is rotated in the normal direction (FIG. 27 A). In this state, when hydraulic brake engagement requirements are satisfied based on a vehicle speed, a steering angle, etc., first, both of the motors are driven so that rotational frequencies of both of the motors become target rotational frequencies (FIG. 27B). The rotational frequencies of both of the motors are brought close to the target rotational frequencies, thus reducing the rotational frequencies of the ring gears and completing rotation adjustment. At this point, the hydraulic brake is engaged, thus fixing the ring gears (FIG. 27C). Then, regeneration is performed by the motor for the left rear wheel serving as an inner wheel at the time of left turning, and the motor for the right rear wheel serving as an outer wheel at the time of left turning is driven (FIG. 27D). Thus, at the time of turning of the vehicle, regeneration can be performed by one of the motors by utilizing a rotation difference between the right and left wheels, and a counterclockwise yawing moment indicated by the hatched arrow in FIG. 27D is exerted on the vehicle.
However, in the control disclosed in WO 2011/013829, the two motors, i.e., the motor for driving the left rear wheel and the motor for driving the right rear wheel, are objects to be controlled, and the rotational frequencies of the motors are different, thus causing a problem that the control is complicated. Further, since both of the motors are driven, there is room for improvement in terms of energy consumption. Moreover, while the rotational frequencies of the ring gears are reduced in order to engage the hydraulic brake, i.e., during a period between a time at which the hydraulic brake engagement requirements are satisfied and a time at which rotation adjustment is completed, no yawing moment is generated as illustrated in FIG. 28.
Furthermore, in the technique disclosed in Japanese Unexamined Patent Application Publication No. 9-79348, when the vehicle is making a turn, the motor for an outer wheel is controlled so as to be driven in the normal (forward) direction and the motor for an inner wheel is controlled so as to be driven in the reverse (opposite) direction, thereby generating a yawing moment in the turning direction and assisting the vehicle in making the turn.
In the vehicle driving apparatus disclosed in Japanese Unexamined Patent Application Publication No. 9-79348, driving control is performed on both of the motors in assisting the vehicle to make a turn. Accordingly, the two motors, i.e., the motor for driving an outer wheel and the motor for driving an inner wheel, are objects to be controlled, and the rotational frequencies of the motors are different, thus causing a problem that the control is complicated. Further, since both of the motors are driven, there is room for improvement in terms of energy consumption.